Semiconductor laser device and method for fabricating the same

Abstract

A semiconductor laser device of the present invention includes: an active layer formed on a substrate; a first semiconductor layer formed on the active layer and made of a nitride semiconductor of a first conductivity type; a multilayer film formed on the first semiconductor layer and having a groove; and a second semiconductor layer formed on the multilayer film to fill the groove and made of a nitride semiconductor of the first conductivity type. The multilayer film is composed of a plurality of thin films containing a nitride semiconductor of a second conductivity type, and one of the thin films formed as the uppermost film is made of gallium nitride.

1. A method for fabricating a semiconductor laser device, said method comprising the steps of:
 successively forming an active layer, a first semiconductor layer made of a nitride semiconductor of a first conductivity type and a multilayer film made of a plurality of thin films containing a nitride semiconductor of a second conductivity type, the uppermost one of said thin films being gallium nitride; 
 forming a groove by selectively removing a part of the multilayer film; and 
 forming a second semiconductor layer made of the nitride semiconductor of the first conductivity type on the multilayer film formed with the groove. 
 
     
     
       2. The method of  claim 1 , wherein
 at least one of the thin films constituting the multilayer film is a thin film containing aluminum other than the upper most one of said thin films, and 
 the thin film containing aluminum has a lower concentration of impurities of the second conductivity than the upper most one of said thin films. 
 
     
     
       3. The method of  claim 2 , wherein
 the thin film containing aluminum is made of a compound expressed by the general formula Al x Ga 1-x N(0<x≦1). 
 
     
     
       4. The method of  claim 1 , wherein
 in the step of forming the groove, a metal mask is formed on the upper most one of said thin films, and then the multilayer film is subjected to wet etching using the formed metal mask. 
 
     
     
       5. The method of  claim 4 , wherein
 the metal mask makes ohmic contact with the upper most one of said thin films. 
 
     
     
       6. The method of  claim 4 , wherein
 the metal mask is made of titanium or tantalum. 
 
     
     
       7. The method of  claim 4 , wherein
 in the step of forming the groove, a metal film made of a metal less likely to be ionized than hydrogen is formed on the top surface of the metal mask after the formation of the metal mask. 
 
     
     
       8. The method of  claim 7 , wherein
 the metal less likely to be ionized than hydrogen is platinum. 
 
     
     
       9. The method of  claim 4 , wherein
 in the step of forming the groove, wet etching is performed while light having higher energy than the thin film of the multilayer film having a larger band gap than the other thin films thereof is applied to the multilayer film. 
 
     
     
       10. The method of  claim 4 , wherein
 in the wet etching, alkaline solution is used as etchant. 
 
     
     
       11. The method of  claim 10 , wherein
 the alkaline solution is aqueous potassium hydroxide or aqueous sodium hydroxide. 
 
     
     
       12. A semiconductor laser device comprising:
 an active layer formed on a substrate; 
 a first semiconductor layer formed on the active layer and made of a nitride semiconductor of a first conductivity type; 
 a multilayer film formed on the first semiconductor layer to have a groove and obtained by stacking a plurality of thin films containing a nitride semiconductor of a second conductivity type, the uppermost one of said thin films being gallium nitride; and 
 a second semiconductor layer formed on the multilayer film to fill the groove and made of a nitride semiconductor of the first conductivity type. 
 
     
     
       13. The device of  claim 12 , wherein
 at least one of the thin films constituting the multilayer film is a thin film containing aluminum other than the upper most one of said thin films, and 
 the thin film containing aluminum has a lower concentration of impurities of the second conductivity type than the upper most one of said thin films. 
 
     
     
       14. The device of  claim 13 , wherein
 the thin film containing aluminum is made of an undoped nitride semiconductor. 
 
     
     
       15. The device of  claim 13 , wherein
 the thin film containing aluminum is made of a compound expressed by the general formula Al x Ga 1-x N(0<x≦1). 
 
     
     
       16. The device of  claim 12 , wherein
 the upper most one of said thin films has a thickness of 5 nm through 0.3 μm both inclusive. 
 
     
     
       17. The device of  claim 12 , wherein
 the second semiconductor layer has a larger refractive index than one of the thin films having the smallest refractive index than one of the thin films having the smallest refractive index. 
 
     
     
       18. The method of  claim 15 , wherein
 the thin film containing aluminum is made of a compound expressed by the general formula Al x Ga 1-x N(0.1≦x≦0.4).